The present invention relates to improvements in dry shavers, particularly rotary type dry shavers. More particularly, the present invention relates to improvements in the shaving unit of rotary type dry shavers. Rotary type dry shavers are shavers in which the shaving unit comprises a shaving head (sometimes referred to as an outer cutter blade body) and an inner cutter (sometimes referred to as an inner cutter blade body) over which the shaving head is mounted. Typically, the shaving head includes a thin, perforated metal plate referred to as a comb (or outer cutter blade) which is pressed against the skin during operation of the shaver, the perforations permitting whiskers and hair to pass through the comb. The inner cutter includes a rotatable base (sometimes referred to as an inner cutter blade base) on which cutter blades (sometimes referred to as inner cutter blades) are mounted radially about the axis of rotation of the base. The cutting edges of these cutter blades are in contact or nearly in contact with the perforated metal comb over substantially their entire length. (The inner cutter blades are thus substantially perpendicular to the inner surface of the comb.) On rotation of the base, the cutter blades rotate past the perforations of the comb and cut any hair or whiskers which has passed those perforations. Typically, the rotatable base is rotated by means of an electric motor, and hence these shavers are often referred to as rotary type electric shavers. An example of a rotary type electric shaver is described in U.S. Pat. No. 3,552,007, issued to Yamada on Jan. 5, 1971, which is hereby incorporated by reference.
Conventional rotary type electric shavers suffer from certain disadvantages relating to the means by which the cutter blades are mounted on the rotatable base. In the conventional mounting, each cutter blade possesses a leg portion which extends away from its cutting edge to what may be called the distal edge of the cutter blade. This distal edge possesses a receiving hole formed from an extension of the center of the distal edge. The leg portion of each cutter blade is inserted through a receiving slit in the rotatable base where it is engaged by a leaf spring mounted on the bottom of the rotatable base, the leaf spring being divided into sub-leaves which resiliently engage the distal edge of the cutter blade including the receiving hole. There is one receiving slit and one associated leaf spring for each cutter blade. Typically, the leaf springs engage their respective cutter blades below the center of gravity of those blades. So mounted, each cutter blade has some freedom of movement in all directions.
Because of this method of mounting, when the shaver is in use, each cutter blade possesses a moment of rotation about an axis passing through its center of gravity and perpendicular to its surface which may be referred to as the cutter blade rotational axis. This axis is perpendicular to the axis of rotation of the rotatable base on which the cutter blade is mounted. The tendency of the cutter blade to rotate about its own rotational axis results in nonuniform contact pressure between the cutting edge of the cutter blade and the comb, resulting in reduced cutting efficiency, uneven wear of the cutting edge of the cutter blade and even breakage of the cutter blade.